Signaling system



" Jane 7, 1949.-

Filed March 7, 1945 H. E. GoLDsTlNE SIGNALING SYSTEM 2 Sheets-Sheet 1 asan excitation unit Patented June 7, 1949 SIGNALING SYSTEM Hallan EugeneGoldstine,

assignor to Radio Co corporation of Delaware -Port Jefferson, N. Y.,rporation of America, a

Application March 7, 1945, Serial No.58l,4l2 6 Claims. (Cl. 332-28) Thisapplication discloses a new and improved resonant line in a new andimproved stabilizing circuit for a ktube wave generator operating atvery yhigh frequencies.

'I'he application also discloses the above stabilized generator in awave frequency modulating system wherein the oscillation generator iscoupled into the said improvedline to generate stabilized oscillationsand wherein the oscillations are modulated as to frequency by amodulator also coupled into the said line, and wherein the timingmodulated oscillatory energy is supplied as excitation or output to afollowing tube or other load circuit by coupling the input of the sameinto the said improved line.

There is much need in the radio art for a simple relatively inexpensivewave generating and wave frequency modulating system that is reliable inoperation, may be operated by a relatively inexperienced operator andwill not get out of order while in service. For example, such a systemis of wide use to our military forces for communicating relatively shortdistances between units and between control points and units, etc. Atransmitter for such use must be of rugged construction and must becapable of operating at its assigned frequency over a considerableperiod of time under varying weather and temperature conditions withoutchanging frequency. In my improved system these requirements and othersare met. Moreoverin my system the generated wave frequency does notchange, even though the potential source may decrease considerably withuse. The advantage of this is apparent. The frequency changingoperations and apparatus are simple and reliable. The transmitter may beof relatively low power. since the same is to be used over distances ofthe order of 40 miles. Although I have described my system as supplyingthe output to a working circuit. it will be understood that the same maybe used to supply amplifiers and/or frequency multipliers in turnfeeding a load.

The ultimate object of my invention is improved transmitter circuits andoperation.

Systems of this general type known heretofore, comprising generators ofvery high i'requency wave energy and frequency modulators for the same,in many cases are too complicated for the need mentioned above. Theyusually include somewhat involved frequency stabilizing apparatus andcircuits and usually make use of several tuning elements and controlsfor freouency changing purposes. These systems re- 2 qulre trainedoperators and must be adjusted and regulated by experienced personnel.

The requirements to be met prevent use of A. F. C. apparatus and yet thesystem needs to be of susbtantially constant mean frequency, which ismaintained under varying temperatures and varying power supply sourcepotentials.

Since the mean frequency of the timing modulated wave energy is to bestabilized, some means for holding the frequency substantially constantis necessary, and a further object of my invention is yan improved'frequency stabilizing means. In my system this means takes the form ofan improved resonant line. My improved resonant stabilizing line, asincluded in the high frequency generating and modulating system inaccordance with my invention, not only simplifies the whole arrangement,as will appear in detail hereinafter, but permits frequency changingadjustments to be made with a minimum number of controls, and in factpermits operation and maintenance by a relatively inexperienced person.

A more speciiic object of my invention is a resonant line or similarhigh Q circuit wherein the resonant frequency to which the line isadjusted remains substantially fixed, irrespective of changes in workingtemperature.

A further object of my invention is a simplified, structurally strongand readily adjustable resonant line wherein the resonant frequencyremains substantially xed irrespective of working temperature changes.

An additional somewhat specific object 'of my invention is an improvedfrequency stabilizing line in -an improved oscillation generatingcircuit with improved means for modulating the frequency of theoscillations generated, and improved means for supplying the generatedfrequency modulated oscillationsto a circuit being excited such as, forexample, an amplifier tube or a multiplier tube, or an antenna, directlyor by way of an ampliiier or multiplier tube.

In describing my invention in detail, reference will be made to theattached drawings, wherein Fig. 1 illustrates by wiring diagram andschematically the essential features of a resonant line, an oscillationgenerator associated therewith to be controlled thereby, modulatingmeans associated with the line and a load circuit excited by energy inthe line.

Fig. 2 illustrates in detail by cross-section the essential features ofa high Q resonant line arranged in accordance with my invention.

Fig. 3 illustrates a resonant line which is a modification of the lineoi' Figs. 1 and 2.

vphysical dimensions of the In Fig. 1 of the drawings L5 is a high Qtemperature compensated circuit in the form of a concentric line. linedescribed with reference to Fig. 2, as well as Fig. 1, comprises anouter member III and an inner member I2 having at the open end enlargedportions l2" and I2"', providing a lumped'eifect at this end so that theline may be less than the electrical dimensions thereof, which are aboutM4. With respect to the tank circuit formed by the line. this largediameter inner conductor may be considered the tank capacitance. The endplug portion I2"' is movable by means of screw I5 and may be considereda variable condenser in parallel with the main condenser formed by I2".and provides the sole tuning means required in the tank circuit fortuning over the required frequency band. Resilient metallic fingers |55make good contact between portions I2" and I2' of the inner conductor.At the other or closed end of the line the inner conductor is of smallerdiameter and may be considered the tank inductance. Coupling loops L5,L1, L5, Ll and LIII are positioned in the resonant line in the spacebetween theinner and outer conductors near the short circuited end. Thelarge spacing between the inner and outer members I and I2 increases thesurge impedance of the line at this end.

The electron discharge devices VI, V2 and V3 each comprise two electrodedischarge systems in a single tube, but it will be understood that eachof these tubes may be replaced by two tubes.

The tube VI is the oscillation generator tube and has its electrodescoupled by the tank I0, I2, and loops L and L1 in an oscillationgenerator of the Meissner t In this generator the control grids IS andI5 are inductively coupled in pushpull relation to the tank circuit byloop L1. The anode electrodes 2l and 22 of the electron dischargesystems in tube VI are coupled difierentially by the loop L5. It will benoted that the connections to the loop L1 are crossed to derive theopposed or 180 phase relation between the grid and anode voltagesnecessary in discharge systems operating as regenerative generators. Thetube and loop couplings as described form a pushpull oscillator which istuned by the resonant frequency control line L5.

Plate potential is supplied by a lead from a power supply source to apoint on the center of the loop L6. The lead is bypassed for radiofrequency by condenser 24. Bias for the control grids is supplied byconnecting a point on the loop L1 through resistors RI and R2 to ground.Unbypassed resistor RI serves to damp parasitic oscillations, while gridleak resistance R2 shunted t by bypass condenser 25 supplies oscillator.

Cathode bias for the tube VI is supplied by resistor RI3. The heatervoltage supply lead terminals marked X-X', the plate voltage lead andthe cathode return lead, to ground through resistor RIB. 'of the tubeVI, are each completed through radio frequency filters which keep theoscillator radio frequency voltage from causing undesired radiation andalso keep radio frequency voltage out of the audio modulation, directcurrent supply and metering circuits. The bypass condensers on theheater, cathode and screen grid terminals of the socket for the tubeused are built into the socket.

The tube V2 is similar in electrode arrangement to the t ube VIL and maybe of the same .......unnn nm-tance grid bias for the 4 tube controlledby signals for modulating the generated oscillations.

The anodes 30 and 32 of the electron discharge devices V2 are coupled inpushpull relation into the resonant circuit by coupling loop Ll. Theplate voltage is fed through the center tap of coupling loop LI by linel5 running through the lter to the positive terminal of a direct currentsource. A condenser 4l is connected from this center tap to ground tobypass radio frequency voltages. The screen grids are also supplied withdirect current from lead 35 through a potential dropping resistanceshunted by a condenser 42 which bypasses audio to keep the same oi! thescreen grids. The control grid coupling loop L! has one end grounded,being thereby connected substantially directly to the cathodes of thedischarge systems in V2. The other end of the loop L9 supplies radiofrequency voltages from the resonant tank circuit L5 to the gridcoupling condensers C5 and C5. These phase shifting condensers are ofabout like size, but one thereof is adjustable in order that thereactance tube sections may be balanced in case the capacitances andgains thereof are different. The two grids are fed in parallel by theradio frequency excitation voltage. The radio frequency voltage isimpressed on each grid across the coils LI and L3 which in combinationwith the resistors R4 and R5 respectively, and condensers C5 and CI formphase shifting networks which shift the grid voltages with respect tothe voltage induced in loop L9. If the plates of the systems are excitedby voltages out of phase with respect to each other and the grids arefed by voltages displaced 90, the phase of the voltage on the grid ofone discharge system will lead the phase of the voltage on the plate ofthe same system 90, and the phase of the voltage on the grid of theother discharge system will lag the phase of the voltage on the -plateof the other system 90. Thus the plate current in one electron dischargesystem will lead the plate voltage 90, this system appearing as acapacitive reactance, and the plate current in the other system will lagthe plate voltage thereof by 90, this system appearing as an inductivereactance.

The reactance tube is connected so Athat when one half of the tube lookslike a capacitive reactance, the other half appears as an inductivereactance. Then when the grids are modulated in pushpull as they are,when the capacitive reactance is decreasing the inductive reactance isincreasing, both operating in a direction to lower the oscillatorfrequency. When the capacitive reactance is increasing in one tube, theinductive reactance cf the other half of the tube is decreasing, bothtending to raise the oscillator frequency. Thus potential variationsapplied to both sections of the tube simultaneously, such as screen gridvoltage variations, hum, etc., do not cause the oscillator frequency tochange, because these effects on the two sections balance andcompensate. For details of this operation. reference y is made to CrosbyU. S. Patent #2,278,429, dated April '7, 1942. p

The condensers C5 and C4 are radio frequency bypass condensers and coilsL2 and L4 are radio frequency choking coils which prevent radiofrequency from getting back into the audio lines 50. The audio frequencyor modulating voltage is fed to the grids through coils L2 and L4 andapplied to the grids through resistor coil combinations LI, R4 and L3,R5. The cathode return by lead 52 is ilrst fed through a radio frequencyfilter which is near the tube socket and keeps the 5 t radio frequencyout of the tube leads and then through a second filter in the illtergroup at 43, and then through cathode bias resistance RI! to ground. n

'I'he generated and frequency modulated oscillations produced in theline L3 and tube VI and frequency modulated by reactance tube V2 aresupplied by loop LIU, in the space between inner and outer conductors III and I2, coupled in pushpull fashion to the control grids 'I0 and I2of a tube V3. In the embodiment tested,l tube V3 operatesas a frequencytripler. The tube V3 may be of the same type as the tubes VI and V2.'I'he advantages of using similar tubes throughout the system will beapparent. Tubes of only one type need be kept for replacement andinterchange throughout the entire system. I'he center tap of the loopLIII is connected to ground by parasitic damping resistor Rl and gridleak resistor R8 shunted by a radio frequency bypass condenser C9. Thecathodes of this tube are tied together and connected by a lead througha radio frequency filter in the group of filters and resistors Ril andR39 to ground. The screen grids of tubes 80 and 82 are supplied bypositive direct current potential through resistor R9, lead 'Il and oneof the R. F. filters of the group of filters. The anodes of these tubesare also supplied direct current potential by ylead 14. The cathodeterminal is as in the prior tubes connected directly lto ground by acondenser for filtering purposes. The resistors RII and R33 supply thecathode bias for the tube.

The plate circuit of the Systems in V3 is composed of rods LII andvariable dual condenser C43, the rotor plates of which are grounded.'Ihe other ends of the rods are connected to the anodes 80 and 82 oftube V3. The plate circuit may be tuned to the fundamental or a harmonicand in the embodiment used this circuit is tuned t the third harmonic ofthe frequency generated by the oscillator in tank L5. The radiofrequency voltage between the rods varies along their length, beinghigher at the ends. The plate direct current voltage is fed throughradio frequency chokes LII at a place where the radio frequency voltageacross the rods LI I is low. The junction point between the radiofrequency coils LI4 is connected directly to ground through a radiofrequency bypassing condenser 33. Parasitic damping resistors R40 andR4I may be used across each of the inductances LH to prevent undesiredoscillations. The length of LII is such as to provide a proper outputimpedance to the tube and to provide with condenser CII tuning over thedesired frequency range.

The output coupling loop LI2 is positioned near the low frequencyvoltage point of the output circuit, this being a point where thecurrent in the circuit is high and provides considerable magneticcoupling in the inductance LI2. 'I'he loop LI2 is fixed tuned bycondenser C42. The radio frequency output from the line LI I is fed fromthe coupling coll LI2 through a short length of coaxial transmissionline or cable CL to radio frequency receptacle PI. The length of theline CL is not critical, as it is part of the transmission line to theantenna, and line CL should have the same surge impedance as thetransmission line.

A diode V4 is coupled to the output coupling loop LI2 by a line LI3 toprovide an indication oi' the radio frequency output voltage. Thisindication appears on meter MI when switch SI is in the radio frequencyposition designated in the drawings RF. One plate of the double diodeVli is connected through the short circuit end of the quarter wavelength section of the radio frequency transmission line LIS. Thissection of the line has an electrical length of about M4 and functionsas an impedance transformer and permits a small amount of the outputvoltage to be impressed on the plate of diode VI, and thus preventssubstantial loading of the output circuit by diode V4. The double diodeVI may be replaced by a single diode tube.

'I'he heaters of the diode V4 are bypassed by condensers CII and CI2.'Ihe cathode IIII of diode Vl which is used is likewise bypassed toground by condenser CIS. This condenser shunts bias resistors RIII andRII connected in series between the cathode and ground. The directcurrent metering voltage is taken across resistor RI I and is fedthrough a filter of the group of filters to switch SI, when in the radiofrequency position RF, through meter MI, then through the resistor RI 6to ground.

'I'he meter MI by means of switch SI is also arranged to indicate thecathode current of the modulation amplifier, not shown, when the switchSI is on the contact labeled AMP. When the switch SI is placed on thecontact labeled .V the volume of the modulator output. not shown, isindicated. The purpose of the contact RF has been described above. Whenthe switch SI is on the contact labeled AMP the cathode current to amodulation amplifier is measured. When the switch SI is on the contactlabeled MOD the current to the cathodes of the devices in the reactancetube V2 is measured. With the switch SI on the contact labeled OSC thecurrent to the cathodes of the oscillator tube VI is measured. and whenswitch SI is on the contact labeled PA the current to the cathodes ofthe power ampli- :Iier V3 is measured.

In my improved system, modulation of any type may be applied byconnecting the modulator output to the leads 50. In the apparatus built,high quality audio channel and low quality audio channel is appliedthrough an improved modulation amplier system not claimed and describedhere- Details of the resonant line L are shown in Fig. 2. The linecomprises the outer member 50 III which may be mounted in any desiredmanner.

In the embodiment built, the outer member Il is flanged at each end andin the center and vbolted at the open end to the rear wall of thetransmitter housing, intermediate the ends to a 55 center panel, and atthe closed end to the inner front wall of the transmitter housing. Themember III may be retained in position in any known manner. In theembodiment built, it is flanged as described and bolted to thetransmitter wall 60 panels and center panels. The inner line I2 isattached to the line closure member` I 09 which is in turn bolted to thefront panel of the transmitter housing by the same bolts fastening lineI3 thereto. 'Ihe flange on which member Il! is 65 bolted, is slightlytapered to provide contact on the inner perimeter of the flange. Thisprovides low contact resistance and reduces variation in the position ofthe contact between the members. The members I0 and I2, in theembodiment con- 70 structed, are cylindrical. Member I2 extends alongthe axis of member III and is enlarged at I2". The enlarged cup-likeportion is welded or brazed or soldered to the reduced' portion I2'. Asecond cup or plug portion I2'" partially within 75 cup portion I2" isjoined to one end of a metallic sleeve I|5, the other to a heavy washeror .similar means ||l bolted to a sleeve III. The sleeve |I9 isthickened at |2| or attached to a heavier sleeve which is threaded onthe inner periphery to cooperate with a square screw thread |32 on ashaft not numbered to move cup or plug member I2'" axially to protrudemore or less from cup section I2" for tuning Pul'POSeS- The snorted endof the outer member Il has a plurality of openings III therein intowhich the loops L6, L1, Ll, L9 and LIO are inserted. In the particularembodiment described, the closed end of the line has five such openingstherein. The coupling loops are mounted on insulating material arrangedin these openings. A loop so mounted is shown at |20. This loop mightwell be the loop L6 or L1 or L8 or L|0 of Fig. 1. However, loop L1 issmaller than loops L5, L0 and LIO. The insulating material |30 loopwithin the opening and also`provides loop terminal and intermediateconnecters |34.

The inner member I2 of the line has a reduced portion I2', a firstenlarged cup shaped cylinder n portion I2", and a second enlarged cupshaped plug portion |2"' which is adjustable. The pluglike adjustableportion I2"' is of larger diameter than-the portion I2', but is smallerthan the portion I2" so that it may be moved in and out of thecylindrical portion I2 to thereby vary the total length of the line andtune the system, as described above. Beryliium copper, silver platedspring contacts |30 are arranged within the inner surface of the portionI2" to make contact with the outer surface of |2" as this movable plugportion is adjusted as to position by the screw member I5. The screwmember |5 is on or attached to a shaft driven by knob or crank |40. Thepinion |38 on the drive shaft drives a larger gear |42 carrying a dialor other indicating means |44 arranged behind an opening in the frontpanel Ill. The gear |42 has its point of rotation at |46 and the dial|44 is calibrated in frequency.

Returning now to the line, the member |2"', as stated above, isadjustable with respect to the member I2" for tuning purposes. A spring|50 at one end bears against the ange member I|1 supporting the plugmember -|2"', and at the other end bears against a member |54 which isfixedly mounted within the inner line portion |2 to force the inner linesection |2'" in its most extended position against the thread screws|32. In other words, the spring |50 prevents an effect here similar toback lash in usual condenser drive arrangements. The screw I5 and itsspindle sleeve are made of Invar to hold the overall length of the lineI2 substantially constant. The smaller cylindrical member or plug member|2" is mounted on a sleeve I fastened to the flange ||1. The cylindricalsleeve or guide member ||5 "slides on the outer surface of the innerline I2. The member -I I5 is made of brass, which has a highercoefficient of expansion than the metal of which the other portions |2'and |2" of the inner conductor I2 is composed. Thus any expanslon of theinner members |2' and I2", excluding portion I2', which takes place withchanges in temperature is compensated by movement of the adjustable plugsection |2"' in an opposite direction, due to expansion of the brassguide member l5, which takes place at a higher rate. The relativelengths of |I.5 and I2' and I2 is such that substantially completecompensation for temperature changes is obtained.

7 end of which is fastened.

supports the In the embodiment built, the line I2. except for theportion II5, is made of cold rolled steel. the surface being silverplated for higher conductivity. The entire line could bemade of Invar,if the same was at hand. When the member I2' and I2" expands the memberIii expands in the opposite direction and thereby tends to compensatefor difference in diameters between the large section l2" and theadjustable plug section |2'".

In the transmitter described, only two controls are used to tune thesystem to lthe desired frequency. To change the frequency of operationwithin the range covered by the system the main tuning knob |40 isturned until the desired reading is shown on the dial |44. This adjuststhe length of the line L5 by adjusting the position of the inner cupmember |2" relative to the fixed parts of the line to thereby tune theline LI. Then the switch BI is moved to close contact RF and thecondenser C43 is tuned for maximum output, indicated in the meter MI.

Although it will be obvious that the tube arrangement, circuit elementetc. depends in large part on the frequency at which it is operated, inthe embodiment constructed the tubes Vl, V2 and V3 are of the type RCA829. The tube V4 is of the type RCA 6H6. The line L5 has a physicallength of about 12 inches. The inner conductor has a physical length ofabout 9" at the high frequency end, and 11" at the low frequency end.The electrical length of a 7i/4 length line at this frequency is about36". The frequency of operation is in the 230 to 250 megacycle band. Theoscillation generator VI operated in the 'I6 to 84 meter band. V3operated as an amplifier and frequency tripler. Modulation from to15,000 cycles per second may be applied. 100% modulation at 100 kc.deviation is obtainable at an output of 10-15 watts.

A modified means for providing temperature compensation is shown in Fig.3. In this embodiment the line may be as shown in Fig. 1, except for theconstruction of the compensating cup |2'" of the line. TheA temperaturecompensation end plug or cup |2"' is of alternate layers or sections ofhigh and low expansion material, folded in such a manner as to increasethe effective overall length of the correcting sleeve member ||5. Thesquare threaded spindle I5 is again of material with a low coefficientof expansion, such as Invar, as is the sleeve I2 I, so that the distancebetween the line ends |09 and ||1 is about constant with changes intemperature. The member |'|5 is of material such as brass, which has ahigh coemcient of expansion. This sleeve ||5 carries a folded backportion H5' made of material such as Invar, which does not materiallyexpand with increases in temperature. This folded portion carries amember I5" made of a material which does expand with changes intemperature. For example, steel may be used here, or if more expansionis desired this member ||5" may be of brass. Now as the steel members I2and I2 expand to cause the cup |2"' to protrude further from cup I2" andlengthen the line, the sleeve I5 expands, as does the member 5", toretract the cup |2'" to compensate the said expansion and hold the totallength of the inner conductor of the line constant.

If the steel parts of the frequency control line are made of steelhaving as low coefficient of expansion as obtainable, and the brass usedfor compensating has a relatively high coeiiicient of expansion, thenthe temperature coeicients of the lines of both embodiments will bogood.

What is claimed is:

1. In a signalling systeml a resonant line comprising two parallelconductors conductively connected together at one end. said conductorshaving portions of close spacing and portions of wide spacing, apparatusfor relatively adjusting-the lengths of the conductors for tuningpurposes, a tube generator having its input and output electrodesregeneratively coupled by loops in the space between said conductors, areactance tube having its output electrodes coupled to a loop in thespace .between said conductors and having its input electrodes coupledto a loop in the space between said conductors, a phase shifting networkin one of said last two couplings, an output tube having inputelectrodes coupled for excitation to a loop in the space between saidconductors, and a load circuit coupledv to said output tube.

2. In a signalling system, a resonant line comprising two parallelconductors conductively connected together at one end, said conductorshaving portions of close spacing and portions of wide spacing, a tubegenerator having its input and output electrodes regeneratively coupledby loops in the'space between said conductors, a reactance tube havingits output electrodes coupled to a loop in the space between saidconductors and having its input electrodes coupled by phase shiftingnetworks to a loop between said conduc tors, connections for applyingmodulating potentials to the input electrodes of said reactance tube, anoutput tube having input electrodes coupled i'or excitation to a loop inthe space between said conductors. a load circuit coupled to said outputtube, and means for varying the eiiective length of one of saidconductors to tune said system.

3. In a signalling system, at least three electron discharge tubesystems, a resonant line comprising two metallic telescoped cylindricalmembers electrically coupled at one end. the inner member comprising aportion of small diameter spaced by considerable distance from the othermember, a portion of large diameter closely spaced to the other memberand a second portion of large diameter physically adjustable in positionrelative to the other portion of large diameter for tuning the line,means for adjusting said second portion of large diameter relative tothe other portion o! large diameter, a regenerative coupling between onetube and said inner member for the production of oscillatory energy. acoupling between said inner member and the input and output electrodesoi' a second one of said tubes such that there is a phase quadraturerelation between the generated voltages on said input and outputelectrodes, means for modulating the gain of said second tube. acoupling between said inner conductor and the input electrodes of thethird tube. and an output circuit coupled to the output electrodes ofthe third tube.

4. In a modulation system. a resonant line comprising two metallictelescoped cylindrical members electrically coupled together at one end.the inner member comprising a portion oi' small diameter spaced byconsiderable distance from the other member. a portion o! large diameterclosely spaced to` the other member and a second portion of large'diameter physically adjustable in posi. tion relative to the otherportion oi' large diameter for tuning the line. means for adjusting saidsecond portion of large diameter relative to the other portion of largediameter, an electron discharge device having input and outputelectrodes. means for coupling said device in a regenerative oscillationgenerator circuit including a first loop between said members coupled tothe output electrodes of said device and a second loop between saidmembers coupled to the input electrodes of said device, and means formodulating the frequency of the oscillations generated including a loopin the space between said members. a reactance coupled to the loop andmeans for varying the reactance in accordance with signals.

5. In a modulation system, a resonant line comprising two metallictelescoped cylindrical members electrically coupled together at one end,the inner member comprising a portion of small diameter spaced byconsiderable distance from the other member, a portion of large diameterclosely spaced to the other member and a second portion of largediameter physically adjustable in position relative to the other portionof large diameter for tuning the line, means for adjusting said secondportion of large diameter relative to the other portion of largediameter, an electron discharge device having input and outputelectrodes, means for coupling said device in a regenerative oscillationgenerator circuit including a first loop between said members coupled tothe output electrodes of said device and a second loop between saidmembers coupled to the input electrodes of said device, a reactance tubehaving input and output electrodes. a loop between said members coupledto said reactance tube output electrodes, a loop between said memberscoupled to said reactance tube input electrodes, a phase shifter in oneof said last two couplings, and a source of modulating potentialscoupled to said reactance tube.

6. In a signaling system. a resonant line comprising two parallelconductors conductively connected together at one end. means forrelatively adjusting the lengths of said conductors to vary the tuningof the resonant circuit formed thereby, an electron discharge tubegenerator having input and output electrodes regeneratively coupled byloops positioned in the space between said conductors, a reactance tubemodulator having input and output electrodes coupled to loops in thespace between said conductors, a phase shifting network in the couplingbetween the input electrodes of said reactance tube and the loop in thespace between said conductors, means ior modulating the gain of saidreactance tube in accordance with signals, and means for deriving outputfrom said tube generator including an output circuit coupled to a loopin the space between said conductors.

` HALLAN EUGENE GOLDSTINE.

REFERENCES CITED The following references are of record in tho ille of4this patent:

UNrrnp STATES PATENTS

